1. Field of Invention
This invention pertains to devices for generating resonance vibrations in the ultrasonic-frequency range, and more particularly to a piezoelectrically excitable resonance system, which can be used to diffuse, spray or atomize liquids.
2. Description of the Prior Art
One device for atomizing liquid described in U.S. Pat. No. 3,904,896 (DE-Al 2,032,433) consists of a metal body having rotational symmetry, and a piezoceramic vibrator coupled to a base area of the metal body. The metal body of this resonance systemm designed for bending excitation has three regions, namely, a disc-shaped base plate, a vibrating plate designating the working plate, and a stem which connects the base plate and the working plate and which coincides with the axis of symmetry of the metal body. The working plate serves, for instance, for containing a liquid. Liquids atomized with such a resonance system have droplet diameters which, generally, are not small enough to penetrate all the way into the lungs of a person. Such a resonance system is therefore not very suitable for atomizing liquids used for inhalation purposes.
For improving the above-mentioned liquid atomizer, it has been proposed in German patent application DE-A-3,616,713 (U.S. Application Ser. No. 049,129) to design the working plate as a concave mirror while the base plate is cone-shaped, and to connect it to the conical base plate via a neck having a special shape. Thereby, very small volumes of liquid (15 microliters or less) can be atomized by using thickness resonance excitation, without a mechanical droplet filter, with a small electric excitation power and without coupling through a liquid medium, to form droplets with a diameter smaller than or equal to 40 micrometers. The vibration frequency of this resonance system is in the megahertz range.